Memory system

ABSTRACT

A memory system includes: a first memory device including a first memory and a first memory controller suitable for controlling the first memory to store data; a second memory device including a second memory and a second memory controller suitable for controlling the second memory to store data; and a processor suitable for executing an operating system (OS) and an application to access a data storage memory through the first and second memory devices.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C § 119(e) to U.S.Provisional Application No. 62/242,831 filed on Oct. 16, 2015, which isincorporated herein by reference in its entirety.

BACKGROUND

1. Field

Various embodiments relate to a memory system and, more particularly, amemory system including plural heterogeneous memories having differentlatencies.

2. Description of the Related Art

In conventional computer systems, a system memory, a main memory, aprimary memory, or an executable memory is typically implemented by thedynamic random access memory (DRAM). The DRAM-based memory consumespower even when no memory read operation or memory write operation isperformed to the DRAM-based memory. This is because the DRAM-basedmemory should constantly recharge capacitors included therein. TheDRAM-based memory is volatile, and thus data stored in the DRAM-basedmemory is lost upon removal of the power.

Conventional computer systems typically include multiple levels ofcaches to improve performance thereof. A cache is a high speed memoryprovided between a processor and a system memory in the computer systemto perform an access operation to the system memory faster than thesystem memory itself in response to memory access requests provided fromthe processor. Such cache is typically implemented with a static randomaccess memory (SRAM). The most frequently accessed data and instructionsare stored within one of the levels of cache, thereby reducing thelumber of memory access transactions and improving performance.

Conventional mass storage devices, secondary storage devices or diskstorage devices typically include one or more of magnetic media (e.g.,hard disk drives), optical media (e.g., compact disc (CD) drive, digitalversatile disc (DVD), etc.), holographic media, and mass-storage flashmemory (e.g., solid state drives (SSDs) removable flash drives, etc.).These storage devices are Input/Output (I/O) devices because they areaccessed by the processor through various I/O adapters that implementvarious I/O protocols, Portable or mobile devices (e.g., laptops,netbooks, tablet computers, personal digital assistant (PDAs), portablemedia players, portable gaming devices, digital cameras, mobile phones,smartphones, feature phones, etc.) may include removable mass storagedevices (e.g., Embedded Multimedia Card (eMMC), Secure Digital (SD)card) that are typically coupled to the processor via low-powerinterconnects and I/O controllers.

A conventional computer system typically uses flash memory devicesallowed only to store data and not to change the stored data in order tostore persistent system information. For example, initial instructionssuch as the basic input and output system (BIOS) images executed by theprocessor to initialize key system components during the boot processare typically stored in the flash memory device. In order to speed upthe BIOS execution speed, conventional processors generally cache aportion of the BIOS code during the pre-extensible firmware interface(PEI) phase of the boot process.

Conventional computing systems and devices include the system memory orthe main memory, consisting of the DRAM, to store a subset of thecontents of system non-volatile disk storage. The main memory reduceslatency and increases bandwidth for the processor to store and retrievememory operands from the disk storage.

The DRAM packages such as the dual in-line memory modules (DIMMs) arelimited in terms of their memory density, and are also typicallyexpensive with respect to the non-volatile memory storage. Currently,the main memory requires multiple DIMMs to increase the storage capacitythereof, which increases the cost and volume of the system. Increasingthe volume of a system adversely affects the form factor of the system.For example, large DIMM memory ranks are not ideal in the mobile clientspace. What is needed is an efficient main memory system whereinincreasing capacity does not adversely affect the form factor of thehost system.

SUMMARY

Various embodiments of the present invention are directed to a memorysystem including plural heterogeneous memories having differentlatencies.

In accordance with an embodiment of the present invention, a memorysystem may include: a first memory device including a first memory and afirst memory controller suitable for controlling the first memory tostore data; a second memory device including a second memory and asecond memory controller suitable for controlling the second memory tostore data and a processor suitable for executing an operating system(OS) and an application to access a data storage memory through thefirst and second memory devices. The first and second memories may beseparated from the processor. The second memory controller may transfera signal between the processor and the second memory device based on atleast one of a value of a handshaking information field included in thesignal. The first memory may include a plurality of first high-capacitymemory cores suitable for working as cache memories for the secondmemory. The first memory device may further include a first memorymanagement logic communicatively and commonly coupled with the pluralityof first high-capacity memory cores, and suitable for supportinghigh-speed data communication between the processor and the plurality offirst high-capacity memory cores. The second memory may include aplurality of second high-capacity memory cores. The second memory devicemay further include a second memory management logic communicatively andcommonly coupled with the plurality of second high-capacity memorycores, and suitable for supporting data communication between theprocessor and the plurality of second high-capacity memory cores. Thesecond memory management logic may include a buffer suitable forbuffering write data to update the plurality of second memory cores. Thesecond memory management logic may firstly buffer the write data in thebuffer, and then independently update the plurality of second memorycores based on the buffered write data.

In accordance with an embodiment of the present invention, a memorysystem may include; a first memory device including a first memory and afirst memory controller suitable for controlling the first memory tostore data; a second memory device including a second memory and asecond memory controller suitable for controlling the second memory tostore data; and a processor suitable for accessing the first and secondmemory. The second memory controller may transfer a signal between theprocessor and the second memory device based on at least one of a valueof a handshaking information field included in the signal. The firstmemory may include a plurality of first high-capacity memory coressuitable for working as cache memories for the second memory. The firstmemory device may further include a first memory management logiccommunicatively and commonly coupled with the plurality of firsthigh-capacity memory cores, and suitable for supporting high-speed datacommunication between the processor and the plurality of firsthigh-capacity memory cores. The second memory may include a plurality ofsecond high-capacity memory cores. The second memory device may furtherinclude a second memory management logic communicatively and commonlycoupled with the plurality of second high-capacity memory cores, andsuitable for supporting data communication between the processor and theplurality of second high-capacity memory cores. The second memorymanagement logic may include a buffer suitable for buffering write datato update the plurality of second memory cores. The second memorymanagement logic may firstly buffer the write data in the buffer, andthen independently update the plurality of second memory cores based onthe buffered write data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically illustrating a structure ofcaches and a system memory according to an embodiment of the presentinvention.

FIG. 2 is a block diagram schematically illustrating a hierarchy ofcache—system memory—mass storage according to an embodiment of thepresent invention.

FIG. 3 is a block diagram illustrating a computer system according to anembodiment of the present invention.

FIG. 4 is a block diagram illustrating a two-level memory sub-systemaccording to an embodiment of the present invention.

FIG. 5 is a block diagram illustrating a first memory of the two-levelmemory sub-system of FIG. 4.

FIG. 6 is a block diagram illustrating a second memory of the two-levelmemory sub-system of FIG. 4.

DETAILED DESCRIPTION

Various embodiments will be described below in more detail withreference to the accompanying drawings. The present invention may,however, be embodied in different forms and should not be construed aslimited to the embodiments set forth herein. Rather, these embodimentsare provided so that this disclosure will be thorough and complete andwill fully convey the scope of the present invention to those skilled inthe art. The drawings are not necessarily to scale and in someinstances, proportions may have been exaggerated to clearly illustratefeatures of the embodiments. Throughout the disclosure, referencenumerals correspond directly to like parts in the various figures andembodiments of the present invention. It is also noted that in thisspecification, “connected/coupled” refers to one component not onlydirectly coupling another component but also indirectly coupling anothercomponent through an intermediate component. In addition, a singularform may include a plural form as long as it is not specificallymentioned in a sentence. It should be readily understood that themeaning of “on” and “over” in the present disclosure should beinterpreted in the broadest manner such that “on” means not only“directly on” but also “on” something with an intermediate feature(s) ora layer(s) therebetween, and that “over” means not only directly on topbut also on top of something with an intermediate feature(s) or alayer(s) therebetween. When a first layer is referred to as being “on” asecond layer or “on” a substrate, it not only refers to a case in whichthe first layer is formed directly on the second layer or the substratebut also a case in which a third layer exists between the first layerand the second layer or the substrate.

FIG. 1 is a block diagram schematically illustrating a structure ofcaches and a system memory according to an embodiment of the presentinvention.

FIG. 2 is a block diagram schematically illustrating a hierarchy ofcache—system memory mass—storage according to an embodiment of thepresent invention,

Referring to FIG. 1, the caches and the system memory may include aprocessor cache 110, an internal memory cache 131 an external memorycache 135 and a system memory 151. The internal and external memorycaches 131 and 135 may be implemented with a first memory 130 (see FIG.3), and the system memory 151 may be implemented with one or more of thefirst memory 130 and a second memory 150 (see FIG. 3).

For example, the first memory 130 may be volatile and may be the DRAM.

For example, the second memory 150 may be non-volatile and may be one ormore of the NAND flash memory, the NOR flash memory and a non-volatilerandom access memory (NVRAM). Even though the second memory 150 may beexemplarily implemented with the NVRAM, the second memory 150 will notbe limited to a particular type of memory device.

The NVRAM may include one or more of the ferroelectric random accessmemory (FRAM) using a ferroelectric capacitor, the magnetic randomaccess memory (MRAM) using the tunneling magneto-resistive (TMR) layer,the phase change random access memory (PRAM) using a chalcogenide alloy,the resistive random access memory (RERAM) using a transition metaloxide, the spin transfer torque random access memory (STT-RAM), and thelike.

Unlike a volatile memory, the NVRAM may maintain its content despiteremoval of the power. The NVRAM may also consume less power than a DRAM.The NVRAM may be of random access. The NVRAM may be accessed at a lowerlevel of granularity (e.g., byte level) than the flash memory. The NVRAMmay be coupled to a processor 170 over a bus, and may be accessed at alevel of granularity small enough to support operation of the NVRAM asthe system memory (e.g., cache line size such as 64 or 128 bytes). Forexample, the bus between the NVRAM and the processor 170 may be atransactional memory bus (e.g., a DDR bus such as DDR3, DDR4, etc.). Asanother example, the bus between the NVRAM and the processor 170 may bea transactional bus including one or more of the PCI express (PCIE) busand the desktop management interface (DMI) bus, or any other type oftransactional bus of a small-enough transaction payload size (e.g.,cache line size such as 64 or 128 bytes). The NVRAM may have fasteraccess speed than other non-volatile memories, may be directly writablerather than requiring erasing before writing data, and may be morere-writable than the flash memory.

The level of granularity at which, the NVRAM is accessed may depend on aparticular memory controller and a particular bus to which the NVRAM iscoupled. For example, in some implementations where the NVRAM works as asystem memory, the NVRAM may be accessed at the granularity of a cacheline (e.g. a 64-byte or 128-Byte cache line), at which a memorysub-system including the internal and external memory caches 131 and 135and the system memory 151 accesses a memory. Thus, when the NVRAM isdeployed as the system memory 151 within the memory sub-system, theNVRAM may be accessed at the same level of granularity as the firstmemory 130 (e.g., the DRAM) included in the same memory sub-system. Evenso, the level of granularity of access to the NVRAM by the memorycontroller and memory bus or other type of bus is smaller than that ofthe block size used by the flash memory and the access size of the I/Osubsystem's controller and bus.

The NVRAM may be subject to the wear leveling operation due to the factthat storage cells thereof begin to wear out after a number of writeoperations. Since high cycle count blocks are most likely to wear outfaster, the wear leveling operation may swap addresses between the highcycle count blocks and the low cycle count blocks to level out memorycell utilization. Most address swapping may be transparent toapplication programs because the swapping is handled by one or more ofhardware and lower-level software (e.g., a low level driver or operatingsystem).

The phase-change memory (PCM) or the phase change random access memory(PRAM or PCRAM) as an example of the NVRAM is a non-volatile memoryusing the chalcogenide glass. As a result of heat produced by thepassage of an electric current, the chalcogenide glass can be switchedbetween a crystalline state and an amorphous state. Recently the PRAMmay have two additional distinct states. The PRAM may provide higherperformance than the flash memory because a memory element of the PRAMcan be switched more quickly the write operation changing individualbits to either “1” or “0” can be done without the need to firstly erasean entire block of cells, and degradation caused by the write operationis slower. The PRAM device may survive approximately 100 million writecycles.

For example, the second memory 150 may be different from the SRAM, whichmay be employed for dedicated processor caches 113 respectivelydedicated to the processor cores 111 and for a processor common cache115 shared by the processor cores 111; the DRAM configured as one ormore of the internal memory cache 131 internal to the processor 170(e.g., on the same die as the processor 170) and the external memorycache 135 external to the processor 170 (e.g., in the same or adifferent package from the processor 170); the flash memory/magneticdisk/optical disc applied as the mass storage (not shown); and a memory(not shown) such as the flash memory or other read only memory (ROM)working as a firmware memory, which can refer to boot ROM and BIOSFlash.

The second memory 150 may work as instruction and data storage that isaddressable by the processor 170 either directly or via the first memory130. The second memory 150 may also keep pace with the processor 170 atleast to a sufficient extent in contrast to a mass storage 251B. Thesecond memory 150 may be placed on the memory bus, and may communicatedirectly with a memory controller and the processor 170.

The second memory 150 may be combined with other instruction and datastorage technologies (e.g., DRAM) to form hybrid memories, such as, forexample, the Co-locating PRAM and DRAM, the first level memory and thesecond level memory, and the FLAM (i.e., flash and DRAM).

At least a part of the second memory 150 may work as mass storageinstead of, or in addition to, the system memory 151. When the secondmemory 150 serves as a mass storage 251A, the second memory 150 servingas the mass storage 251A need not be random accessible, byte addressableor directly addressable by the processor 170.

The first memory 130 may be an intermediate level of memory that haslower access latency relative to the second memory 150 and/or moresymmetric access latency (i.e., having read operation times which areroughly equivalent to write operation times). For example, the firstmemory 130 may be a volatile memory such as volatile random accessmemory (VRAM) and may comprise the DRAM or other high speedcapacitor-based memory. However, the underlying principles of theinvention will not be limited to these specific memory types. The firstmemory 130 may have a relatively lower density. The first memory 130 maybe more expensive to manufacture than the second memory 150.

In one embodiment, the first memory 130 may be provided between thesecond memory 150 and the processor cache 110. For example, the firstmemory 130 may be configured as one or more external memory caches 135to mask the performance and/or usage limitations of the second memory150 including, for example, read/write latency limitations and memorydegradation limitations. The combination of the external memory cache135 and the second memory 150 as the system memory 151 may operate at aperformance level which approximates is equivalent or exceeds a systemwhich uses only the DRAM as the system memory 151.

The first memory 130 as the intern& memory cache 131 may be located onthe same die as the processor 170. The first memory 130 as the externalmemory cache 135 may be located external to the die of the processor170. For example, the first memory 130 as the external memory cache 135may be located on a separate die located on a CPU package, or located ona separate die outside the CPU package with a high bandwidth link to theCPU package. For example, the first memory 130 as the external memorycache 135 may be located on a dual in-line memory module (DIMM), ariser/mezzanine, or a computer motherboard. The first memory 130 may becoupled in communication with the processor 170 through a single ormultiple high bandwidth links, such as the DDR or other transactionalhigh bandwidth links.

FIG. 1 illustrates how various levels of caches 113, 115, 131 and 135may be configured with respect to a system physical address (SPA) spacein a system according to an embodiment of the present invention. Asillustrated in FIG. 1, the processor 170 may include one or moreprocessor cores 111, with each core having its own internal memory cache131. Also, the processor 170 may include the processor common cache 115shared by the processor cores 111. The operation of these various cachelevels are well understood in the relevant art and will not be describedin detail here.

For example, one of the external memory caches 135 may correspond to oneof the system memories 151, and serve as the cache for the correspondingsystem memory 151. For example, some of the external memory caches 135may correspond to one of the system memories 151, and serve as thecaches for the corresponding system memory 151. In some embodiments, thecaches 113, 115 and 131 provided within the processor 170 may performcaching operations for the entire SPA space.

The system memory 151 may be visible to and/or directly addressable bysoftware executed on the processor 170. The cache memories 113, 115, 131and 135 may operate transparently to the software in the sense that theydo not form a directly-addressable portion of the SPA space while theprocessor cores 111 may support execution of instructions to allowsoftware to provide some control (configuration, policies, hints, etc.)to some or all of the cache memories 113, 115, 131 and 135.

The subdivision into the plural system memories 151 may be performedmanually as part of a system configuration process (e.g., by a systemdesigner) and/or may be performed automatically by software.

In one embodiment, the system memory 151 may be implemented with one ormore of the non-volatile memory (e.g., PRAM) used as the second memory150, and the volatile memory (e.g., DRAM) used as the first memory 130.The system memory 151 implemented with the volatile memory may bedirectly addressable by the processor 170 without the first memory 130serving as the memory caches 131 and 135.

FIG. 2 illustrates the hierarchy of cache—system memory—mass storage bythe first and second memories 130 and 150 and various possible operationmodes for the first and second memories 130 and 150.

The hierarchy of cache—system memory—mass storage may comprise a cachelevel 210, a system memory level 230 and a mass storage level 250, andadditionally comprise a firmware memory level (not illustrated).

The cache level 210 may include the dedicated processor caches 113 andthe processor common cache 115, which are the processor cache.Additionally, when the first memory 130 serves in a cache mode for thesecond memory 150 working as the system memory 151B, the cache level 210may further include the internal memory cache 131 and the externalmemory cache 135.

The system memory level 230 may include the system memory 151Bimplemented with the second memory 150. Additionally, when the firstmemory 130 serves in a system memory mode, the system memory level 230may further include the first memory 130 working as the system memory151A.

The mass storage level 250 may include one or more of theflash/magnetic/optical mass storage 251B and the mass storage 215Aimplemented with the second memory 150.

Further the firmware memory level may include the BIOS flash (notillustrated) and the BIOS memory implemented with the second memory 150.

The first memory 130 may serve as the caches 131 and 135 for the secondmemory 150 working as the system memory 151B in the cache mode. Further,the first memory 130 may serve as the system memory 151A and occupy aportion of the SPA space in the system memory mode.

The first memory 130 may be partitionable, wherein each partition mayindependently operate in a different one of the cache mode and thesystem memory mode. Each partition may alternately operate between thecache mode and the system memory mode. The partitions and thecorresponding modes may be supported by one or more of hardware,firmware, and software. For example, sizes of the partitions and thecorresponding modes may be supported by a set of programmable rangeregisters capable of identifying each partition and each mode within amemory cache controller 270.

When the first memory 130 serves in the cache mode for the system memory151B, the SPA space may be allocated not to the first memory 130 workingas the memory caches 131 and 135 but to the second memory 150 working asthe system memory 151B. When the first memory 130 serves in the systemmemory mode, the SPA space may be allocated to the first memory 130working as the system memory 151A and the second memory 150 working asthe system memory 151B.

When the first memory 130 serves in the cache mode for the system memory151B, the first memory 130 working as the memory caches 131 and 135 mayoperate in various sub-modes under the control of the memory cachecontroller 270. In each of the sub-modes, a memory space of the firstmemory 130 may be transparent to software in the sense that the firstmemory 130 does not form a directly-addressable portion of the SPAspace. When the first memory 130 serves in the cache mode, the sub-modesmay include but may not be limited as of the following table 1.

TABLE 1 MODE READ OPERATION WRITE OPERATION Write-Back Allocate on CacheMiss Allocate on Cache Miss Cache Write-Back on Evict Write-Back onEvict of Dirty Data of Dirty Data 1^(st) Memory Bypass to 2^(nd) MemoryBypass to 2^(nd) Memory Bypass 1^(st) Memory Allocate on Cache MissBypass to 2^(nd) Memory Read-Cache & Cache Line InvalidationWrite-Bypass 1^(st) Memory Allocate on Cache Miss Update Only on CacheHit Read-Cache & Write-Through to 2^(nd) Memory Write-Through

During the write-back cache mode, part of the first memory 130 may workas the caches 131 and 135 for the second memory 150 working as thesystem memory 151B. During the write-back cache mode, every writeoperation is directed initially to the first memory 130 working as thememory caches 131 and 135 when a cache line, to which the writeoperation is directed, is present in the caches 131 and 135. Acorresponding write operation is performed to update the second memory150 working as the system memory 151B only when the cache line withinthe first memory 130 working as the memory caches 131 and 135 is to bereplaced by another cache line.

During the first memory bypass mode, all read and write operationsbypass the first memory 130 working as the memory caches 131 and 135 andare performed directly to the second memory 150 working as the systemmemory 151B. For example, the first memory bypass mode may be activatedwhen an application is not cache-friendly or requires data to beprocessed at the granularity of a cache lines. In one embodiment, theprocessor caches 113 and 115 and the first memory 130 working as thememory caches 131 and 135 may perform the caching operationindependently from each other consequently the first memory 130 workingas the memory caches 131 and 135 may cache data, which is not cached orrequired not to be cached in the processor caches 113 and 115, and viceversa. Thus, certain data required not to be cached in the processorcaches 113 and 115 may be cached within the first memory 130 working asthe memory caches 131 and 135.

During the first memory read-cache and write-bypass mode,a read cachingoperation to data from the second memory 150 working as the systemmemory 151B may be allowed. The data of the second memory 150 working asthe system memory 151B may be cached in the first memory 130 working asthe memory caches 131 and 135 for read-only operations. The first memoryread-cache and write-bypass mode may be useful in the case that mostdata of the second memory 150 working as the system memory 151B is “readonly” and the application usage is cache-friendly.

The first memory read-cache and write-through mode may be considered asa variation of the first memory read-cache and write-bypass mode. Duringthe first memory read-cache and write-through mode, the write-hit mayalso be cached as well as the read caching. Every write operation to thefirst memory 130 working as the memory caches 131 and 135 may cause awrite operation to the second memory 150 working as the system memory151B. Thus, due to the write-through nature of the cache, cache-linepersistence may be still guaranteed.

When the first memory 130 works as the system memory 151A, all or partsof the first memory 130 working as the system memory 151A may bedirectly visible to an application and may form part of the SPA space.The first memory 130 working as the system memory 151A may be completelyunder the control of the application. Such scheme may create thenon-uniform memory address (NUMA) memory domain where an applicationgets higher performance from the first memory 130 working as the systemmemory 151A relative to the second memory 150 working as the systemmemory 151B. For example, the first memory 130 working as the systemmemory 151A may be used for the high performance computing (HPC) andgraphics applications which require very fast access to certain datastructures.

In an alternative embodiment, the system memory mode of the first memory130 may be implemented by pinning certain cache lines in the firstmemory 130 working as the system memory 151A, wherein the cache lineshave data also concurrently stored in the second memory 150 working asthe system memory 151B.

Although not illustrated, parts of the second memory 150 may be used asthe firmware memory. For example, the parts of the second memory 150 maybe used to store BIOS images instead of or in addition to storing theBIOS information in the BIOS flash. In this case, the parts of thesecond memory 150 working as the firmware memory may be a part of theSPA space and may be directly addressable by an application executed onthe processor cores 111 while the BIOS flash may be addressable throughan I/O sub-system 320.

To sum up, the second memory 150 may serve as one or more of the massstorage 215A and the system memory 151B. When the second memory 150serves as the system memory 151B and the first memory 130 serves as thesystem memory 151A, the second memory 150 working as the system memory151B may be coupled directly to the processor caches 113 and 115. Whenthe second memory 150 serves as the system memory 151B but the firstmemory 130 serves as the cache memories 131 and 135, the second memory150 working as the system memory 151B may be coupled to the processorcaches 113 and 115 through the first memory 130 working as the memorycaches 131 and 135. Also, the second memory 150 may serve as thefirmware memory for storing the BIOS images.

FIG. 3 is a block diagram illustrating a computer system 300 accordingto an embodiment of the present invention.

The computer system 300 may include the processor 170 and a memory andstorage sub-system 330.

The memory and storage sub-system 330 may include the first memory 130,the second memory 150, and the flash/magnetic/optical mass storage 251B.The first memory 130 may include one or more of the cache memories 131and 135 working in the cache mode and the system memory 151A working inthe system memory mode. The second memory 150 may include the systemmemory 151B, and may further include the mass storage 251A as an option.

In one embodiment, the NVRAM may be adopted to configure the secondmemory 150 including the system memory 151B, and the mass storage 251Afor the computer system 300 for storing data instructions, states, andother persistent and non-persistent information.

Referring to FIG. 3, the second memory 150 may be partitioned into thesystem memory 151B and the mass storage 251A, and additionally thefirmware memory as an option.

For example, the first memory 130 working as the memory caches 131 and135 may operate as follows during the write-back cache mode.

The memory cache controller 270 may perform the look-up operation inorder to determine whether the read-requested data is cached in thefirst memory 130 working as the memory caches 131 and 135.

When the read-requested data is cached in the first memory 130 workingas the memory caches 131 and 135, the memory cache controller 270 mayreturn the read-requested data from the first memory 130 working as thememory caches 131 and 135 to a read requestor (e.g., the processor cores111).

When the read-requested data is not cached in the first memory 130working as the memory caches 131 and 135, the memory cache controller270 may provide a second memory controller 311 with the data readrequest and a system memory address. The second memory controller 311may use a decode table 313 to translate the system memory address to aphysical device address (PDA) of the second memory 150 working as thesystem memory 151B, and may direct the read operation to thecorresponding region of the second memory 150 working as the systemmemory 151B. In one embodiment, the decode table 313 may be used for thesecond memory controller 311 to translate the system memory address tothe PDA of the second memory 150 working as the system memory 151B, andmay be updated as part of the wear leveling operation to the secondmemory 150 working as the system memory 151B. Alternatively a part ofthe decode table 313 may be stored within the second memory controller311.

Upon receiving the requested data from the second memory 150 working asthe system memory 151B, the second memory controller 311 may return therequested data to the memory cache controller 270, the memory cachecontroller 270 may store the returned data in the first memory 130working as the memory caches 131 and 135 and may also provide thereturned data to the read requester. Subsequent requests for thereturned data may be handled directly from the first memory 130 workingas the memory caches 131 and 135 until the returned data is replaced byanother data provided from the second memory 150 working as the systemmemory 151B.

During the write-back cache mode when the first memory 130 works as thememory caches 131 and 135, the memory cache controller 270 may performthe look-up operation in order to determine whether the write-requesteddata is cached in the first memory 130 working as the memory caches 131and 135. During the write-back cache mode, the write-requested data maynot be provided directly to the second memory 150 working as the systemmemory 151B For example, the previously write-requested and currentlycached data may be provided to the second memory 150 working as thesystem memory 151B only when the location of the previouslywrite-requested data currently cached in first memory 130 working as thememory caches 131 and 135 should be re-used for caching another datacorresponding to a different system memory address. In this case, thememory cache controller 270 may determine that the previouslywrite-requested data currently cached in the first memory 130 working asthe memory caches 131 and 135 is currently not in the second memory 150working as the system memory 151B, and thus may retrieve the currentlycached data from first memory 130 working as the memory caches 131 and135 and provide the retrieved data to the second memory controller 311.The second memory controller 311 may look up the PDA of the secondmemory 150 working as the system memory 151B for the system memoryaddress, and then may store the retrieved data into the second memory150 working as the system memory 151B.

The coupling relationship among the second memory controller 311 and thefirst and second memories 130 and 150 of FIG. 3 may not necessarilyindicate particular physical bus or particular communication channel. Insome embodiments, a common memory bus or other type of bus may be usedto communicatively couple the second memory controller 311 to the secondmemory 150. For example, in one embodiment, the coupling relationshipbetween the second memory controller 311 and the second memory 150 ofFIG. 3 may represent the DDR-typed bus, over which the second memorycontroller 311 communicates with the second memory 150. The secondmemory controller 311 may also communicate with the second memory 150over a bus supporting a native transactional protocol such as the PCIEbus, the DMI bus, or any other type of bus utilizing a transactionalprotocol and a small-enough transaction payload size (e.g., cache linesize such as 64 or 128 bytes)

In one embodiment, the computer system 300 may include an integratedmemory controller 310 suitable for performing a central memory accesscontrol for the processor 170. The integrated memory controller 310 mayinclude the memory cache controller 270 suitable for performing a memoryaccess control to the first memory 130 working as the memory caches 131and 135, and the second memory controller 311 suitable for performing amemory access control to the second memory 150.

In the illustrated embodiment, the memory cache controller 270 mayinclude a set of mode setting information which specifies variousoperation mode (e.g., the write-back cache mode, the first memory bypassmode etc.) of the first memory 130 working as the memory caches 131 and135 for the second memory 150 working as the system memory 151B. Inresponse to a memory access request, the memory cache controller 270 maydetermine whether the memory access request may be handled from thefirst memory 130 working as the memory caches 131 and 135 or whether thememory access request is to be provided to the second memory controller311, which may then handle the memory access request from the secondmemory 150 working as the system memory 151B.

In an embodiment where the second memory 150 is implemented with PRAM,the second memory controller 311 may be a PRAM controller. Despite thatthe PRAM is inherently capable of being accessed at the granularity ofbytes, the second memory controller 311 may access the PRAM-based secondmemory 150 at a lower level of granularity such as a cache line (e.g., a64-bit or 128-bit cache line) or any other level of granularityconsistent with the memory sub-system. When PRAM-based second memory 150is used to form a part of the SPA space, the level of granularity may behigher than that traditionally used for other non-volatile storagetechnologies such as the flash memory, which may only perform therewrite and erase operations at the level of a block (e.g., 64 Kbytes insize for the NOR flash memory and 16 Kbytes for the NAND flash memory).

In the illustrated embodiment, the second memory controller 311 may readconfiguration data from the decode table 313 in order to establish theabove described partitioning and modes for the second memory 150. Forexample, the computer system 300 may program the decode table 313 topartition the second memory 150 into the system memory 151B and the massstorage 251A. An access means may access different partitions of thesecond memory 150 through the decode table 313. For example, an addressrange of each partition is defined in the decode table 333.

In one embodiment, when the integrated memory controller 310 receives anaccess request, a target address of the access request may be decoded todetermine whether the request is directed toward the system memory 151B,the mass storage 251A, or I/O devices.

When the access request is a memory access request, the memory cachecontroller 270 may further determine from the target address whether thememory access request is directed to the first memory 130 working as thememory caches 131 and 135 or to the second memory 150 working as thesystem memory 151B. For the access to the second memory 150 working asthe system memory 151B, the memory access request may be forwarded tothe second memory controller 311.

The integrated memory controller 310 may pass the access request to theI/O sub-system 320 when the access request is directed to the I/Odevice. The I/O sub-system 320 may further decode the target address todetermine whether the target address points to the mass storage 251A ofthe second memory 150, the firmware memory of the second memory 150, orother non-storage or storage I/O devices. When the further decodedaddress points to the mass storage 251A or the firmware memory of thesecond memory 150, the I/O sub-system 320 may forward the access requestto the second memory controller 311.

The second memory 150 may act as replacement supplement for thetraditional DRAM technology in the system memory. In one embodiment, thesecond memory 150 working as the system memory 151B along with the firstmemory 130 working as the memory caches 131 and 135 may represent atwo-level system memory. For example, the two-level system memory mayinclude a first-level system memory comprising the first memory 130working as the memory caches 131 and 135 and a second-level systemmemory comprising the second memory 150 working as the system memory151B.

According to some embodiments, the mass storage 251A implemented withthe second memory 150 may act as replacement or supplement for theflash/magnetic/optical mass storage 251B. In some embodiments, eventhough the second memory 150 is capable of byte-level addressability,the second memory controller 311 may still access the mass storage 251Aimplemented with the second memory 150 by units of blocks of multiplebytes (e.g. 64 Kbytes, 128 Kbytes, and so forth). The access to the massstorage 251A implemented with the second memory 150 by the second memorycontroller 311 may be transparent to an application executed by theprocessor 170. For example, even though the mass storage 251Aimplemented with the second memory 150 is accessed differently from theflash/magnetic/optical mass storage 251B, the operating system may stilltreat the mass storage 251A implemented with the second memory 150 as astandard mass storage device (e.g., a serial ATA hard drive or otherstandard form of mass storage device).

In an embodiment where the mass storage 251A implemented with the secondmemory 150 acts as replacement or supplement for theflash/magnetic/optical mass storage 251B, it may not be necessary to usestorage drivers for block-addressable storage access. The removal of thestorage driver overhead from the storage access may increase accessspeed and may save power. In alternative embodiments where the massstorage 251A implemented with the second memory 150 appears asblock-accessible to the OS and/or applications and indistinguishablefrom the flash/magnetic/optical mass storage 251B, block-accessibleinterfaces (e.g., Universal Serial Bus (USB), Serial Advanced TechnologyAttachment (SATA) and the like) may be exposed to the software throughemulated storage drivers in order to access the mass storage 251Aimplemented with the second memory 150.

In some embodiments, the processor 170 may include the integrated memorycontroller 310 comprising the memory cache controller 270 and the secondmemory controller 311 all of which may be provided on the same chip asthe processor 170, or on a separate chip and/or package connected to theprocessor 170.

In some embodiments, the processor 170 may include the I/O sub-system320 coupled to the integrated memory controller 310. The I/O sub-system320 may enable communication between processor 170 and one or more ofnetworks such as the local area network (LAN), the wide area network(WAN) or the Internet; a storage I/O device such as theflash/magnetic/optical mass storage 251B and the BIOS flash; and one ormore of non-storage I/O devices such as display, keyboard, speaker, andthe like. The I/O sub-system 320 may be on the same chip as theprocessor 170, or on a separate chip and/or package connected to theprocessor 170.

The I/O sub-system 320 may translate a host communication protocolutilized within the processor 170 to a protocol compatible withparticular I/O devices.

In the particular embodiment of FIG. 3, the memory cache controller 270and the second memory controller 311 may be located on the same die orpackage as the processor 170. In other embodiments, one or more of thememory cache controller 270 and the second memory controller 311 may belocated off-die or off-package, and may be coupled to the processor 170or the package over a bus such as a memory bus such as the DDR bus thePCIE bus, the DMI bus, or any other type of bus.

FIG. 4 is a block diagram illustrating a two-level memory sub-system 400according to an embodiment of the present invention.

Referring to FIG. 4, the two-level memory sub-system 400 may include thefirst memory 130 working as the memory caches 131 and 135 and the secondmemory 150 working as the system memory 151B. The two-level memorysub-system 400 may include a cached sub-set of the mass storage level250 including run-time data. In an embodiment the first memory 130included in the two-level memory sub-system 400 may be volatile and theDRAM. In an embodiment, the second memory 150 included in the two-levelmemory sub-system 400 may be non-volatile and one or more of the NANDflash memory, the NOR flash memory and the NVRAM. Even though the secondmemory 150 may be exemplarily implemented with the NVRAM, the secondmemory 150 will not be limited to a particular memory technology.

The second memory 150 may be presented as the system memory 151B to ahost operating system (OS: not illustrated) while the first memory 130works as the caches 131 and 135, which is transparent to the OS, for thesecond memory 150 working as the system memory 151B. The two-levelmemory sub-system 400 may be managed by a combination of logic andmodules executed via the processor 170. In an embodiment, the firstmemory 130 may be coupled to the processor 170 through high bandwidthand low latency means for efficient processing. The second memory 150may be coupled to the processor 170 through low bandwidth and highlatency means.

The two-level memory sub-system 400 may provide the processor 170 withrun-time data storage. The two-level memory sub-system 400 may providethe processor 170 with access to the contents of the mass storage level250. The processor 170 may include the processor caches 113 and 115,which store a subset of the contents of the two-level memory sub-system400.

The first memory 130 may be managed by the memory cache controller 270while the second memory 150 may be managed by the second memorycontroller 311. In an embodiment, the memory cache controller 270 andthe second memory controller 311 may be located on the same die orpackage as the processor 170. In other embodiments, one or more of thememory cache controller 270 and the second memory controller 311 may belocated off-die or off-package, and may be coupled to the processor 170or to the package over a bus such as a memory bus (e.g., the DDR bus),the PCIE bus, the DMI bus, or any other type of bus.

The second memory controller 311 may report the second memory 150 to thesystem OS as the system memory 151B. Therefore, the system OS mayrecognize the size of the second memory 150 as the size of the two-levelmemory sub-system 400. The system OS and system applications are unawareof the first memory 130 since the first memory 130 serves as thetransparent caches 131 and 135 for the second memory 150 working as thesystem memory 151B.

The processor 170 may further include two-level management unit 410 Thetwo-level management unit 410 may be a logical construct that maycomprise one or more of hardware and micro-code extensions to supportthe two-level memory sub-system 400. For example, the two-levelmanagement unit 410 may maintain a full tag table that tracks the statusof the second memory 150 working as the system memory 151B. For example,when the processor 170 attempts to access a specific data segment in thetwo-level memory sub-system 400 the two-level management unit 410 maydetermine whether the data segment is cached in the first memory 130working as the caches 131 and 135. When the data segment is not cachedin the first memory 130, the two-level management unit 410 may fetch thedata segment from the second memory 150 working as the system memory151B and subsequently may write the fetched data segment to the firstmemory 130 working as the caches 131 and 135. Because the first memory130 works as the caches 131 and 135 for the second memory 150 working asthe system memory 151B, the two-level management unit 410 may furtherexecute data prefetching or similar cache efficiency processes known inthe art.

The two-level management unit 410 may manage the second memory 150working as the system memory 151B. For example, when the second memory150 comprises the non-volatile memory, the two-level management unit 410may perform various operations including wear-leveling, bad-blockavoidance, and the like in a manner transparent to the system software.

As an exemplified process of the two-level memory sub-system 400, inresponse to a request for a data operand, it may be determined whetherthe data operand is cached in first memory 130 working as the memorycaches 131 and 135. When the data operand is cached in first memory 130working as the memory caches 131 and 135, the operand may be returnedfrom the first memory 130 working as the memory caches 131 and 135 to arequestor of the data operand. When the data operand is not cached infirst memory 130 working as the memory caches 131 and 135, it may bedetermined whether the data operand is stored in the second memory 150working as the system memory 151B. When the data operand is stored inthe second memory 150 working as the system memory 151B, the dataoperand may be cached from the second memory 150 working as the systemmemory 151B into the first memory 130 working as the memory caches 131and 135 and then returned to the requestor of the data operand. When thedata operand is not stored in the second memory 150 working as thesystem memory 151B, the data operand may be retrieved from the massstorage 250, cached into the second memory 150 working as the systemmemory 151B, cached into the, first memory 130 working as the memorycaches 131 and 135, and then returned to the requestor of the dataoperand.

In accordance with an embodiment of the present invention, signalsexchanged between the processor 170 and a second memory unit, whichincludes the second memory controller 311 and the second memory 150working as the system memory 151B, may include a handshaking informationfield as well as a memory access request field and a correspondingresponse field (e.g., the read command, the write command, the address,the data, the data strobe, and so forth).

The handshaking information field may be for the second memory unit,which includes the second memory controller 311 and the second memory150 working as the system memory 151B, communicating with the processor170 through the handshaking scheme, and therefore may be included in thesignal exchanged between the processor 170 and the second memory unit,which includes the second memory controller 311 and the second memory150 working as the system memory 151B. For example, the handshakinginformation field may have three values according to types of the signalbetween the processor 170 and the second memory unit (the second memorycontroller 311 and the second memory 150 working as the system memory151B) as exemplified in the following table 2.

TABLE 2 HANDSHAKING FIELD SOURCE DESTINATION SIGNAL TYPE 10 PROCESSOR(170) 2^(ND) MEMORY UNIT DATA REQUEST (READ COMMAND) 11 2^(ND) MEMORYUNIT PROCESSOR (170) DATA READY 01 PROCESSOR (170) 2^(ND) MEMORY UNITSESSION START

As exemplified in table 2 the signals between the processor 170 and thesecond memory unit may include at least the data request signal (“DATAREQUEST (READ COMMAND)”), the data ready signal (“DATA READY”), and thesession start signal (“SESSION START”), which have binary values “10”,“11” and “01” of the handshaking information field, respectively.

The data request: signal may be provided from the processor 170 to thesecond memory unit, and may indicate a request of data stored in thesecond memory unit. Therefore, for example, the data request signal mayinclude the read command and the read address as well as the handshakinginformation field having the value “10” indicating the second memoryunit as the destination.

The data ready signal may be provided from the second memory unit to theprocessor 170 in response to the data request signal, and may have thehandshaking information field of the value “11” representingtransmission standby of the requested data, which is retrieved from thesecond memory unit in response to the read command and the read addressincluded in the data request signal.

The session start signal may be provided from the processor 170 to thesecond memory unit in response to the data ready signal, and may havethe handshaking information field of the value “01” representingreception start of the requested data ready to be transmitted in thesecond memory unit. For example the processor 170 may receive therequested data from the second memory unit after providing the sessionstart signal to the second memory unit.

The processor 170 and the second memory controller 311 of the secondmemory unit may operate according to the signals between the processor170 and the second memory unit by identifying the type of the signalsbased on the value of the handshaking information field.

Although not illustrated, the second memory controller 311 may furtherinclude a handshaking interface unit. The handshaking interface unit mayreceive the data request signal provided from the processor 170, whichincludes the memory cache controller 270, and having the value “10” ofthe handshaking information field, and allow the second memorycontroller 311 to operate according to the data request signal. Also,the handshaking interface unit may provide the processor 170 with thedata ready signal having the value “01” of the handshaking informationfield in response to the data request signal from the processor 170.

As described above, the bus between the handshaking interface unit andthe processor 170 may be a transactional bus including one or more ofthe PCIE bus and the DMI bus, or any other type of transactional bus ofa mall-enough transaction payload size (e.g., cache line size such as 64or 128 bytes). For example, when the second memory 150 works as thesystem memory 151B, the second memory 150 may be accessed at thegranularity of a cache line (e.g., a 64-byte or 128-Byte cache line), atwhich a memory sub-system including the first memory 130 working as theexternal memory caches 131 and 135 and the system memory 151 accesses amemory. Thus, when the second memory 150 is deployed as the systemmemory 151B within the memory sub-system, the second memory 150 may beaccessed at the same level of granularity as the first memory 130 (e.g.the DRAM) included in the same memory sub-system. The couplingrelationship between the second memory controller 311 and the secondmemory 150 of FIGS. 4 and 5 may not necessarily indicate particularphysical bus or particular communication channel. In some embodiments, acommon memory bus or other type of bus may be used to communicativelycouple the second memory controller 311 to the second memory 150. Forexample, in an embodiment, the coupling relationship between the secondmemory controller 311 and the second memory 150 of FIG. 4 may representa DDR-typed bus, over which the second memory controller 311communicates with the second memory 150. The second memory controller311 may also communicate with the second memory 150 over a bussupporting a native transactional protocol such as the PCIE bus, the DMIbus, or any other type of bus utilizing a transactional protocol and asmall-enough transaction payload size (e.g., cache line size, such as 64or 128 bytes).

Although not illustrated, the second memory controller 311 may furtherinclude a register. The register may temporarily store the requesteddata retrieved from the second memory 150 working as the system memory151B in response to the data request signal from the processor 170. Thesecond memory controller 311 may temporarily store the requested dataretrieved from the second memory 150 working as the system memory 151Binto the register and then provide the processor 170 with the data readysignal having the value “01” of the handshaking information field inresponse to the data request signal.

As an exemplified process of the two-level memory sub-system 400, theprocessor 170 including the memory cache controller 270 may provide thesecond memory controller 311 with the data request signal including thehandshaking information field of the value “10” as well as the readcommand and the read address through the handshaking interface unit. Inresponse to the data request signal, the second memory controller 311may read out requested data from the second memory 150 working as thesystem memory 151B according to the read command and the read addressincluded in the data request signal. The second memory controller 311may temporarily store the read-out data into the register. The secondmemory controller 311 may provide the processor 170 with the data readysignal through the handshaking interface unit after the temporal storageof the read-out data into the register. In response to the data readysignal, the processor 170 may provide the second memory controller 311with the session start signal including the handshaking informationfield of the value “01”, and then receive the read-out data temporarilystored in the register.

As described above, in accordance with an embodiment of the presentinvention, the processor 170 may communicate with the second memory unitthrough the communication of the handshaking scheme and thus theprocessor 170 may perform another operation without stand-by untilreceiving requested data from the second memory unit.

When the processor 170 provides the second memory controller 311 withthe data request signal through the handshaking interface unit, theprocessor 170 may perform another data communication with another device(e.g., the I/O device coupled to the bus coupling the processor 170 andthe handshaking interface unit) until the second memory controller 311provides the processor 170 with the data ready signal. Further, uponreception of the data ready signal provided from the second memorycontroller 311, the processor 170 may receive the read-out datatemporarily stored in the register of the second memory controller 311by providing the session start signal to the second memory controller311 at any time the processor 170 requires the read-out data.

Therefore in accordance with an embodiment of the present invention, theprocessor 170 may perform another operation without stand-by untilreceiving requested data from the second memory unit thereby improvingoperation bandwidth thereof.

FIG. 5 is a block diagram illustrating the first memory 130 of thetwo-level memory sub-system 400 of FIG. 4.

Referring to FIG. 5 the first memory 130 serving as the memory caches131 and 135 may include a first memory management logic 510 and one ormore first memory cores 520A to 520N. The first memory management logic510 may be operatively coupled to the processor 170 through highbandwidth and low latency means.

The first memory cores 520A to 520N may be operatively coupled to oneanother in parallel. The parallel first memory cores 520A to 520N may beoperatively coupled to the first memory management logic 510. Therespective first memory cores 520A to 520N may be a volatile memory coresuitable for high-capacity data caching operation, and may be the DRAMcore. The respective first memory cores 520A to 520N may operate withhigh latency, high caching capacitance, low cost and small powerconsumption. The respective first memory cores 520A to 520N of the firstmemory 130 may operate with higher operation speed than the secondmemory 150. The memory cache controller 270 may control the respectivefirst memory cores 520A to 520N.

The first memory management logic 510 may achieve a relatively highoperation speed of the first memory 130 by compensating for the highlatency of the respective first memory cores 520A to 520N. The firstmemory management logic 510 may support high-speed communication betweenthe processor 170 and the first memory cores 520A to 520N.

The memory cache controller 270 may provide the first memory 130 servingas the memory caches 131 and 135 with a command, an address, a chipaddress, and a clock, and exchange data and a data strobe signal withthe first memory 130.

The command may include a chip select signal, an active signal a rowaddress strobe signal, a column address strobe signal, a write enablesignal, a clock enable signal and the like. Examples of the operationswhich the memory cache controller 270 instructs the first memorymanagement logic 510 to perform through the command may include anactive operation, a read operation, a write operation, a prechargeoperation, a refresh operation, and the like. The chip address maydesignate one or more memory cores to be accessed or to perform a reador write operation among the first memory cores 520A to 520N, and theaddress may designate the location of a memory cell to be accessedinside the selected memory core. The clock may be supplied to the firstmemory 130 from the memory cache controller 270 for the synchronizedoperation of the first memory management logic 510 and the first memorycores 520A to 520N. The data strobe signal for strobing the data may betransmitted to the first memory 130 from the memory cache controller 270during a write operation, and transmitted to the memory cache controller270 from the first memory 130 during a read operation. That is, thetransmission directions of the data strobe signal and the data may bethe same as each other. The clock and the data strobe signal may betransmitted in a differential manner.

The first memory management logic 510 and the first memory cores 520A to520N may be stacked in the first memory 130, and signal transmissionamong the first memory management logic 510 and the first memory cores520A to 520N may be performed through interlayer channels. Theinterlayer channel may be implemented with a through-silicon via (TSV).The memory cache controller 270 and the first memory 130 may directlycommunicate with each other by using the first memory management logic510, and the first memory cores 520A to 520N may indirectly communicatewith the memory cache controller 270 through the first memory managementlogic 510. That is, the signal channels (i.e., the command, address,chip address, clock, data and data strobe signal) between the memorycache controller 270 and the first memory 130 may be connected only tothe first memory management logic 510.

During a write operation, write data transmitted to the first memory 130may be serial-to-parallel converted and then stored in a memory cell ofone or more selected among the first memory cores 520A to 520N. Thewrite data may be processed by the first memory management logic 510 andthen transferred to the selected memory cores. During a read operation,data read from one or more selected among the first memory cores 520A to530N may be parallel-to-serial converted and then transferred to thememory cache controller 270. The read data may be processed by the firstmemory management logic 510 and then transferred to the memory cachecontroller 270. That is, during the write and read operations, theoperations of processing data, that is, the serial-to-parallelconversion and the parallel-to-serial conversion may be performed by thefirst memory management logic 510.

FIG. 6 is a block diagram illustrating the second memory 150 of thetwo-level memory sub-system 400 of FIG. 4.

Referring to FIG. 6, the second memory 150 serving as the system memory151B may include a second memory management logic 610 and one or moresecond memory cores 620A to 620N. The second memory management logic 610may be operatively coupled to the second memory controller 311 throughhigh bandwidth and low latency means.

The second memory cores 620A to 620N may be operatively coupled to oneanother in parallel. The parallel second memory cores 620A to 620N maybe operatively coupled the second memory management logic 610. Therespective second memory cores 620A to 620N may be a non-volatile memorycore, and may be one or more of the NAND flash memory core, the NORflash memory core, and the non-volatile random access memory (NVRAM)core. The respective second memory cores 620A to 620N may work asinstruction and data storage that is addressable by the processor 170either directly or via the first memory 130. The respective secondmemory cores 620A to 620N may keep pace with the processor 170 at leastto a sufficient extent in contrast to the mass storage 251B. Therespective second memory cores 620A to 620N may be placed on the memorybus, and may communicate directly with the second memory controller 311and the processor 170. The respective second memory cores 620A to 620Nmay operate with high latency, high caching capacitance, low cost andsmall power consumption. The respective second memory cores 620A to 620Nof the second memory 150 may operate with lower operation speed than ahigh-speed operation memory such as the first memory 130. The secondmemory controller 311 may control the respective second memory cores620A to 620N.

The second memory management logic 610 may achieve a relatively highoperation speed of the second memory 150 by compensating for the highlatency of the respective second memory cores 620A to 620N. The secondmemory management logic 610 may support high-speed communication betweenthe processor 170 and the second memory cores 620A to 620N.

The second memory controller 311 may provide the second memory 150serving as the system memory 151B with a command, an address, a chipaddress and a dock, and exchange data and a data strobe signal with thesecond memory 150.

The second memory management logic 610 and the second memory cores 620Ato 620N may be stacked in the, second memory 150, and signaltransmission among the second memory management logic 610 and the secondmemory cores 620A to 620N may be performed through interlayer channels.The interlayer channel may be implemented with a through-silicon via(TSV). The second memory controller 311 and the second memory 150 maydirectly communicate with each other by using the second memorymanagement logic 610, and the second memory cores 620A to 620N mayindirectly communicate with the second memory controller 311 through thesecond memory management logic 610. That is, the signal channels (i.e.,command, address, chip address, clock, data and data strobe signal)between the second memory controller 311 and the second memory 150 maybe connected only to the second memory management logic 610.

During a write operation, write data transmitted to the second memory150 may be serial-to-parallel converted and then stored in a memory cellof one or more selected among the second memory cores 620A to 620N. Thewrite data may be processed by the second memory management logic 610and then transferred to the selected memory cores. During a readoperation, data read from one or more selected among the second memorycores 620A to 620N may be parallel-to-serial converted and thentransferred to the second memory controller 311. The read data may beprocessed by the second memory management logic 610 and then transferredto the second memory controller 311. The second memory management logic610 may include a buffer 630.

According to an embodiment of the present invention, in thewrite-through mode of the first memory 130 working as the memory caches131 and 135, the buffer 630 may secure the update time of the secondmemory cores 620A to 620N.

The buffer 630 may have a predetermined buffering capacity and mayoperate according to the first-in-first-out (FIFO) scheme, and thus maybuffer the write data at the same speed as the first memory 130 workingas the memory caches 131 and 135 stores therein the write data. Thebuffer 630 may additionally include a register for enlarged bufferingsize in order to prevent a stall due to a burst write operation

After the buffer 630 buffers therein the write data to be updated, thesecond memory cores 620A to 620N may perform the update operation basedon the write data sequentially buffered in the buffer 630 through thesecond memory management logic 610.

Upon cache hit in the write-through mode of the first memory 130 workingas the memory caches 131 and 135 during the write operation, theprocessor 170 may cache the cache-hit write data in the first memory 130working as the memory caches 131 and 135 without consideration of thelatency of the second memory 150 working as the system memory 151B.Further, the second memory controller 311 may buffer the write data inthe buffer 630 according to the FIFO scheme. During the bufferingoperation, the second memory controller 311 may buffer the write data inthe buffer 630 substantially at the same speed as caching of the writedata in the first memory 130 working as the memory caches 131 and 135.Then, the second memory management logic 610 may update the secondmemory cores 620A to 620N based on the write data buffered in the buffer630 when the buffer 630 is full of the write data or the two-levelmemory sub-system 400 is in an idle state.

Upon cache miss in the write-through mode of the first memory 130working as the memory caches 131 and 135 during the write operation, thesecond memory controller 311 may buffer the cache-missed write data inthe buffer 630 according to the FIFO scheme without caching thecache-missed write data in the first memory 130 working as the memorycaches 131 and 135. Then, the second memory management logic 610 mayupdate the second memory cores 620A to 620N based on the write databuffered in the buffer 630 when the buffer 630 is full of the write dataor the two-level memory sub-system 400 is in an idle state.

In an embodiment, the second memory controller 311 and the second memorymanagement logic 610 may receive from the processor 170 the write dataand then transfer the write data without modification to the secondmemory cores 620A to 620N. For example, upon receiving a stream of thewrite data including plural segments from outside (e.g., an externalsource) the memory system including the processor 170, the second memorycontroller 311 and the two-level memory sub-system 400, the secondmemory controller 311 may buffer the write data in the buffer 630 andthe second memory management logic 610 may update the second memorycores 620A to 620N when needed.

It is not when the write data is updated in the second memory cores 620Ato 620N but when the write data is buffered in the buffer 630 that asignal indicating storage of the write data in the second memory cores620A to 620N is returned to the outside. Therefore, the time required tostore the provided write data in the second memory cores 620A to 620Nmay be reduced, and subsequent write data may be provided faster fromthe outside.

Subsequent write data may be provided from the outside without waitingfor storage completion of previous write data into the second memorycores 620A to 620N. Through the second memory controller 311 and thesecond memory management logic 610, the processor 170 may provide asecond portion of the write data from the outside to the write buffer501 at the same time that the processor 170 is providing a first portionof the write data from the buffer 630 to the second memory cores 620A to620N. Hence, the buffer 630 may allow effective storage of write dataprovided from the outside to the second memory cores 620A to 620N.

For example, 8 segments (e.g. first to eighth segments) of the writedata may be buffered sequentially in the buffer 630 before stored in thesecond memory cores 620A to 620N, which is faster than directly storingthem in the second memory cores 620A to 620N. Instead of waiting forstorage completion of the first segment of the write data into thesecond memory cores 620A to 620N, a signal may be returned to indicatethat the first segment of the write data is stored in the second memorycores 620A to 620N and the second segment of the write data is to beprovided. Such process may be repeated until all of the 8 segments ofthe write data are buffered in the buffer 630 while in a parallel waythe 8 segments of the write data buffered in the buffer 630 are storedin the second memory cores 620A to 620N.

For example, the previously buffered segments of the write data may bestored in the second memory cores 620A to 620N while the currentlyprovided segments of the write data are buffered in the buffer 630.

The sequential segments of the write data are sequentially provided toand buffered in the buffer 630 while the sequential segments of thewrite data buffered in the buffer 630 may be individually provided toand stored in the second memory cores 620A to 620N. The sequentialsegments of subsequent write data are sequentially provided to andbuffered in the buffer 630 while in a parallel way the sequentialsegments of previous write data buffered in the buffer 630 may beprovided to and stored in the second memory cores 620A to 620N.

The amount of time for buffering the provided write data in the buffer630 may be smaller than the amount of time for storing the bufferedwrite data in the second memory cores 620A to 620N.

In an embodiment, non-sequential data segments of a plurality ofindividual write data may be preferentially buffered in the buffer 630.For example, a non-sequential data segment 7 may be promptly stored inthe second memory cores 620A to 620N through the buffer 630 upon beingprovided from the outside. While the non-sequential data segment 7 isbeing buffered in the buffer 630, subsequent and non-sequential datasegments 8 to 16 may be provided from the outside.

The subsequent and non-sequential data segments 8 to 16 may be stored inthe second memory cores 620A to 620N after the previous non-sequentialdata segment 7 is stored in the second memory cores 620A to 620N.

Consequentially, the performance of the memory system including thetwo-level memory sub-system 400 may be improved by the buffer 630 duringthe write operation regardless of the cache hit or cache miss. Duringthe write operation, the write data may be preferably buffered in thebuffer 630 and then the second memory cores 620A to 620N may be updatedaccording to the write data buffered in the buffer 630 regardless of thecache hit or cache miss,

While the present invention has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and or scope of the invention as defined in thefollowing claims.

What is claimed is:
 1. A memory system comprising: a first memory deviceincluding a first memory and a first memory controller configured tocontrol the first memory to store data; a second memory device includinga second memory and a second memory controller configured to control thesecond memory to store data; and a processor is configured to execute anoperating system (OS) and an application to access a data storage memorythrough the first and second memory devices, wherein the first andsecond memories are separated from the processor, wherein the secondmemory controller transfers a signal between the processor and thesecond memory device based on at least one of values of a handshakinginformation field included in the signal, wherein the first memoryincludes a plurality of first high-capacity memory cores configured towork as cache memories for the second memory, wherein the first memorydevice further includes a first memory management logic operatively andcommonly coupled with the plurality of first high-capacity memory cores,and configured to support high-speed data communication between theprocessor and the plurality of first high-capacity memory cores, whereinthe second memory includes a plurality of second high-capacity memorycores configured to work as system memories, wherein the second memorydevice further includes a second memory management logic operatively andcommonly coupled with the plurality of second high-capacity memorycores, and configured to support data communication between theprocessor and the plurality of second high-capacity memory cores,wherein the second memory management logic includes a buffer configuredto buffer write data, based on which the plurality of second memorycores are updated, wherein the second memory controller firstly buffersthe write data in the buffer, and then the second memory managementlogic independently updates the plurality of second memory cores basedon the buffered write data, and wherein the at least one of values ofthe handshaking information field indicates the signal as one of a datarequest signal from the processor to the second memory, a data readysignal from the second memory to the processor and a session startsignal from the processor to the second memory.
 2. The memory system ofclaim 1, wherein the second memory controller includes: a handshakinginterface configured to transfer the signal between the second memorydevice and the processor; and a register configured to temporarily storedata read out from the second memory.
 3. The memory system of claim 1,wherein the data request signal includes a command and an address forthe second memory device.
 4. The memory system of claim 1, wherein thesecond memory controller includes a storage unit, and wherein the secondmemory controller reads data from the second memory and temporarilystores the read data in the storage unit in response to the data requestsignal.
 5. The memory system of claim 4, wherein the second memorycontroller provides the data ready signal to the processor when thesecond memory controller temporarily stores the read data in the storageunit in response to the data request signal.
 6. The memory system ofclaim 5, wherein the processor provides the session start signal toreceive the read data temporarily stored in the storage unit in responseto the data ready signal.
 7. The memory system of claim 1, wherein thefirst memory device is a volatile memory device.
 8. The memory system ofclaim 1, wherein the second memory device is a nonvolatile memorydevice.
 9. The memory system of claim 8, wherein the nonvolatile memorydevice is a nonvolatile random access memory device.
 10. A memory systemcomprising: a first memory device including a first memory and a firstmemory controller configured to control the first memory to store data;a second memory device including a second memory and a second memorycontroller configured to control the second memory to store data; and aprocessor configured to access the first and second memories, whereinthe second memory controller transfers a signal between the processorand the second memory device based on at least one of values of ahandshaking information field included in the signal, wherein the firstmemory includes a plurality of first high-capacity memory coresconfigured to work as cache memories for the second memory, wherein thefirst memory device further includes a first memory management logicoperatively and commonly coupled with the plurality of firsthigh-capacity memory cores, and configured to support high-speed datacommunication between the processor and the plurality of firsthigh-capacity memory cores, wherein the second memory includes aplurality of second high-capacity memory cores configured to work assystem memories, wherein the second memory device further includes asecond memory management logic operatively and commonly coupled with theplurality of second high-capacity memory cores, and configured tosupport data communication between the processor and the plurality ofsecond high-capacity memory cores, wherein the second memory managementlogic includes a buffer configured to buffer write data, based on whichthe plurality of second memory cores are updated, wherein the secondmemory controller firstly buffers the write data in the buffer, and thensecond memory management logic independently updates the plurality ofsecond memory cores based on the buffered write data, and wherein the atleast one of values of the handshaking information field indicates thesignal as one of a data request signal from the processor to the secondmemory, a data ready signal from the second memory to the processor anda session start signal from the processor to the second memory.
 11. Thememory system of claim 10, wherein the second memory controllerincludes: a handshaking interface configured to transfer the signalbetween the second memory device and the processor; and a registerconfigured to temporarily store data read out from the second memory.12. The memory system of claim 11, wherein the data request signalincludes a command and an address for the second memory device.
 13. Thememory system of claim 11, wherein the second memory controller includesa storage unit, and wherein the second memory controller reads data fromthe second memory and temporarily stores the read data in the storageunit in response to the data request signal.
 14. The memory system ofclaim 13, wherein the second memory controller provides the data readysignal to the processor when the second memory controller temporarilystores the read data in the storage unit in response to the data requestsignal.
 15. The memory system of claim 14, wherein the processorprovides the session start signal to receive the read data temporarilystored in the storage unit in response to the data ready signal.
 16. Thememory system of claim 10, wherein the first memory device is a volatilememory device.
 17. The memory system of claim 10, wherein the secondmemory device is a nonvolatile memory device.
 18. The memory system ofclaim 17, wherein the nonvolatile memory device is a nonvolatile randomaccess memory device.